yes that's perfectly right. But the value of the currency should then become indexed to the cost of securing the ledger over the long run. At this point I would think that's it not the case for btc. IMHO developing ASICs for SHA256 hashing is not a grand development for humanity; it's an expected capitalist response to the fact the the p2p system is valuable. It's a capitalistic proof of the bitcoin protocol.

But as a ledger gets bigger it gets more expensive to secure and harder to use; at one point the best economic alternative is to start a new one, based on the same principle, but not the same POW. And then start a new one. So the value resides in the p2p protocol not the currency itself which is a temporary corollary store that exists while the network is growing.